2Jose E. Schutt‐Aine‐ECE 442•Why Use Feedback?1. To desensitize the gain2. To reduce nonlinear distortion3. To reduce the effect of noise4. To control terminal impedances5. To increase the bandwidthFeedback

3Jose E. Schutt‐Aine‐ECE 442Feedback – Basic Concepts

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5Jose E. Schutt‐Aine‐ECE 442()outinoutinvAvvGvβ=−=1==+outinvAGiainoutvvvWhen the switch is closed, thenFeedback – Analysisso thatfrom which we getThe closed-loop gain is always less than the open-loop gain for negative feedbackwhich is the closed-loop gain

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7Jose E. Schutt‐Aine‐ECE 442The feedback amplifier will have a midband gain ofFeedback – Bandwidth Extensionand an upper 3-dB frequency of(1)β+MMAA)ω+HMABandwidth is increased by factor equal to amount of feedback. It can also be shown that the lower 3dB frequency is )+LMAThe gain-bandwidth product is constant

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